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lpril25, 1912. 



U. S. DEPARTMENT OF AGRICULTURE 

BUREAU OF ENTOMOLOGY CIRCULAR No. 150. 

L. O. HOWARD. Entomologist and Chief of Burecu. 



THE RED SPIDER ON (X)TTON. 



bY 



E. A. MCGREGOR, 

Si i< rUifie Assi 



32120 Clr. 150 L2 



WASHINGTON : GOVERNMENT PRINTING I 




BUREAU OF EXTOMOLOGY. 

L. O. Howard, Entomologist and Chief of Bureau. 

C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. 

R. S. Clifton, Executive Assistant. 

W. F. Tastet, Chief Clerk. 

F. H. Chittenden, in charge of truck crop and stand product insect investigations. 

A. D. Hopkins, //* charge of forest insect investigations. 

W. D. Hunter, in charge of southern field crop insect investigations. 

F. M. Webster, in charge of cereal and fgrag( insect investigations. 

A. L. Quaintance, in charge of deciduous fruit insect investigations. 

E. F, Phillips, in charge of bee culture. 

D. M. Rogers, in charge of preventing spread of moths, field work. 
Rolla P. Currie, in charge of editorial work. 

Mabel Colcord, in. charge of library. 

Southern Field Crop Insect Investigations. 
W. I). Hunter, in charge. 

F. C. Bishopp, A. II. Jennings, H. 1". Wood, W. V. King, engaged in tick life- 
history investigations. 

W. D. Pierce, G. D. Smith, J. D. Mitchell, Harry I'inkus. R. R. Coad, R. W. 

Moreland, engaged in cotton-boll weevil investigations. 
A. C. Morgan, G. A. Runner, S. E. Ckumb, D. C. Parman, engaged in tobacco 

insect investigations. 
T. E. Holloway, E. R. Barber, engaged in sugar-cane insect investigations. 

E. A. McGregor, W. A. Thomas, engaged in red spider and other cotton insect 
investigations. 

J. L. Webb, engaged in rice insect investigations. 

R. A. Cooley, D. L. Van Dine, A. F. Conbadi, C. C. Krumbiiaar. collaborators. 

n 



Circular No. 150. 



I--u. d April '25, 1912 



United States Department of Agriculture, 

BUREAU OF ENTOMOLOGY, 
L. O. HOWARD, Entomologist and Chief of Bureau. 



THE BED SPIDER ON COTTON. 1 

• -anychua bimaculatus Harvej | 

By K. A. M< i rBl GOB, 

Scientific Assistant. 
IN CRODl I rORY. 

The minute, reddish spinning mite commonly known as .the red 
spider is rapidly assuming a position of importance among cotton 
pests. At Batesburg, S. C, in L911, it 
first became noticeable on cotton about 
June 1. causing little more than passing 
notice at that time among the farmers, 
hut by the 1st of .Inly it had increased so 
enormously that the effect upon cotton 
in certain places was most alarming. 
Season- of excessive drought greatly fa 
vor the multiplication of the mites until 
the resulting injuries are often so severe 
as to cause the death of many plants. 

Red-spider infestation is frequently 
miscalled " rust " by farmers, since in- 
fested Leaves soon turn deep red on their 
upper surface Such leaves, however, if 
examined underneath, reveal the pres- 
ence of the red spiders and the incon- 
spicuous webs behind which the}' are 
feeding and laying their eggs. 



HISTORY AND IMS lit MUTTON. 




I'n:. 1. 'I'h.' red spider, Tet- 
ranychus bimaculatus: Adult 
Female. Greatly enl 
i Banks.) 



With the exception of an outbreak in 
Louisiana, reported by Prof. II. A. Mor- 
gan in IS!)!'), severe Occurrence of the cotton red spider had not 

been reported until L903, at which time complaints of damage came 

1 This circular i- based primarily upon wort done at Batesburg, s. c. in 1911, 
under the direction "f Mr. \v. D. Hunter, but also Includes the results of observations 
bj Messrs. Q a Runner mid II. l\ Wilson during the two preceding 



2 THE RED SPIDER ON COTTON. 

from South Carolina and Georgia. In 1904 Mr. E. S. G. Titus, 1 
then of this bureau, found severe infestation in fields about Bates- 
burg, S. C.j and the following year he reported severe injury in 
North Carolina, South Carolina, Georgia, and Alabama. Since 
then the additional records of Dr. F. H. Chittenden 2 and Messrs. 
G. P. Weldon, D. T. Fullaway, and others establish the presence 
of the common red spider in Maine. Massachusetts, New York. New 
Jersey, District of Columbia, Virginia, North Carolina, South Caro- 
lina, Georgia, Florida, Alabama, Mississippi. Louisiana. Texas. Ohio, 
western Colorado, Wyoming, Idaho, "Washington, California, and 
the Hawaiian Islands. 

The red spider was described by Harvey 3 in 1893 as Tetranychus 
8-maculatus. Harvey considered it quite distinct from the European 
species T. telarius L. His types were from Orono, Me. In 1907 Prof. 
H. A. Morgan published observations on the cotton mite, and ap- 
parently accepted the determination of the species as T. telarius. 
In 1900 Mr. Nathan Banks described the cotton mite under a dis- 
tinct name — Tetranychus gloveri — but from the study of additional 
specimens has now concluded that the name is synonymous with 
Harvey's T. bimaculatus. Specimens of red spiders on cotton from 
South Carolina have upon two recent occasions been determined by 
Prof. A. Berlese as the continental species — Tetranychus telarius. 
As there seems to be considerable doubt on this point, we shall follow 
Mr. Banks in considering the form with which we are dealing as 
Tetranyc Jinx bimaculatus, 

DESCRIPTION. 

The typical female (fig. 1) is 0.46 mm. long by 0.24 mm. wide, 
broad-oval, widest in front, and the legs are shorter than the body. 
Its color is usually brick-red. The typical male is 0.27 mm. long by 
0.15 mm. wide, oval-wedge shape, narrowed behind, the legs about 
equaling the length of the body, and its color is usually reddish 
amber. Individuals of both sexes usually possess on either side of 
the body a dark spot, caused by the food contents. This spot may 
vary greatly in color, size, and outline. Similarly, depending upon 
the host plant and upon locality, the general color of the red spider 
is subject to great variation. 

The eggs are very minute, but in proportion to the mites they are 
large. They are perfectly round, and when first laid are as clear as 
water. Each female lays (in the months of June. July, and August) 
about 50 to 60 eggs, depositing about 6 per day for a period of about 
nine days. Less than 3 eggs or more than 9 are rarely deposited each 

' Cir. 65, Bur. Ent., U. S. Dept. Agr., 1905. 

-Cir. 104, Bur. Ent., U. S. Dept. Agr., 1905. 

a Ann. Kept. Maine Agr. Exp. Sta. for 1892, Pt. IV, pp. i::.i-14G. 



THE RED SPIDER on COTTON. 6 

day in summer weather. During the warmer months the eggs hatch 
in about four days after being laid. 
The newly hatched red spider, called the Larva, is almost round, 

has si\ Legs, and is nearly colorless. It begins feeding at once, and 

(in summer time) after two day-' activity it becomes quiet, darkens 
in color, casts it- skin for the first time, and emerges as the primary 
nymph with an added pair of Legs making eight. 

The primary nymph becomes Larger in size and darker in color, 
hut gives no indication of sex. Feeding continues ad ively and at the 
termination of another two-day period (in summer months) a second 
molting occurs which gives rise to the third stage -the secondary 
nymph. 

With this last nyinpnal stage the first indication of sex appears. 
As with the preceding stage.-, two day-- usually suffice in summer 
for the completion of this period, at the end of which time the 
skin in shed for the third time and at last the perfectly developed 
adult mites appeal-. At the occurrence of each molt the skin splits in 
two, crosswise, and the creature crawls out of the two halves. The 
old cast skin- are usually to be -ecu in abundance among the fibrils 
of the web. 

THE ADULT MALES AND FEMALES COMPARED. 

Concerning the relative abundance of female- and males it may be 
said that there sixmus to be a predominance of females throughout 
the stimmer. but toward the approach of cold weather the occurrence 
of the sexes becomes more nearly equal. The period of life of the 
adult female varies from 17 days in midsummer to several months 
in winter. The male i- shorter lived. A- before stated, the female 
is decidedly larger than the male, more rounded behind, and of a 
much deeper Color. She doe.-, not move aboul much, and when she 
does her motion is rather slow. On the other hand, when not mating, 
the male i- frequently seen moving rapidly about. The body and 
are well besel with bristles, which arc somewhat more con 
spicuous in tl'.e mall-, than in the females. The eye-, consisting each 
of two Mil,-, one close behind the other, are situated near the front 
edge of the body directly over the second pair of legs. 

M VTING. 

Almost immediately upon becoming adult, the red spiders mate 
aiul begin egg laying. The males seem to recognize unfertilized 
female- with ease. The tir-i eggs are frequently deposited on the 
same day upon which the transformation occurs from the last 
liymphal to the adult stage. 



THE RED SPIDER ON COTTON. 



PARTHENOGENESIS. 

Experiments conducted with unmated female red spiders clearly 
proved that they are normally capable of laying eggs, which in turn 
hatch and develop into mature individuals. No tests, however, have 
been successfully conducted to determine the sexual fertility of the 
latter. 

GENERATIONS. 

The season of 1911 at Batesburg, S. C, was one of unusual drought 
and heat and there were about 17 generations between March 11 and 
November 5. The time required for a single generation varied from 
35 days in March and early April to 10 days throughout most of 
June, July, and August, and to 25 days in the greater portion of 
October and early November. The following table presents the 
duration of each stage of each of the 17 generations: 

Table I. — Development of generation* of the cotton red spider. 



Gener- 
ation. 



1 

2. 
3 
4 
5 
ti 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 



l'eriod covered by gerneration. 



Incuba- 
tion 
period. 



Mar. 11 to Apr. 14. 
Apr. 15 to Apr. 29. 
Apr. 30 to May 13. 
May 14 to May 25. . 
May 20 to June 6.. 
June 7 to June 17. 
June IS to June 27. 
June 28 to July 7.. 
JulvSto July 18... 
July 19 to July 28. . 
July 29 to Aug. 7. . 
Aug. 8 to Aug. 17.. 
Aug. IS to Aug. 29. 
Aug. 30 to Sept. 9. 
Sept. 10 to Sept. 24 
Sept. 25 to Oct. 10. 
Oct. 11 to Nov. 4.. 

Average 



Days. 
13 
6 
6 
5 
5 

4.5 
4 
4 
4 
4 
4 
4 
5 
5 
5 




5.5 



Larval 
period. 



Days. 
9 
3 
3 
3 
3 

2.5 
2 
2 

2.5 
2 
2 
2 

2.5 
2 

3.5 
3 




3.1 



Nymph 

(1) 
period. 



Days. 

3 
3 
2 
2 
2 
2 
2 

2.5 
2 
2 
2 
2 
2 
3 
3 
5 



Nymph 

(2) 
period. 



Days. 
7 
3 
2 
2 
2 
2 
2 
2 
2 
2 
2 
2 

2.5 
2 

3.5 
4 
5 



2.8 



Ovipo- 

sition to 

adult. 



Days. 



35 
15 
11 
l-> 
12 
11 
10 
10 
11 
10 
10 
10 
12 
11 
15 
\i< 
25 



11 



RELATION OF WEATHER TO BREEDING ACTIVITIES. 

The influence of the weather on breeding activity is very notice- 
able. Hot, dry conditions greatly favor and hasten development. 
while cool, wet weather correspondingly retards it. A female laying 
normally about 6 or 7 eggs per day will often upon the occurrence 
of a very hot day, suddenly increase the number to 15 or even more 
eggs per day, or upon a chilly day may drop as suddenly to 1 or 2 
eggs. It is easy then to understand the remarkable rate at which 
this pest increases during times of unusual drought. 

OBSERVATIONS ON HABITS. 

In establishing herself upon cotton the female selects a concave 
area between the uinlcr v"eins of the leaf and begins at once to deposit 
e<s<^. These may be attached to the fibrils of the web slightly above 
the surface, or, as seems most often the case, they are placed directly 



THE RED SIMM i; <>N rorinN. 



upon the Leaf. The eggs are usually clustered rather closely and 
rarely occupy an area greater in size than that of a dime. Feeding 
continues interruptedly throughout the period of egg Laying and the 
affected area of the leaf becomes thickly dotted with the blackish- 
green puncture marks. Meanwhile a wine-red spot has appeared on 
the upper surface of the Leaf directly over the young colony, which 
spreads as the colony increases and may finally color the entire Leaf. 
As the eggs hatch the larva' remain close to the place of their birth. 
The mite- seem of a decidedly social disposition. In a young colony 
there is usually little web formed, but where the spiders are very 
abundant the web may become quite conspicuous. It doubtless 
afford- some protection from adverse weather conditions, and upon 
several occasion- hostile insects have been observed ensnared and dead 
among the fibers. New females, after mating, either select an attrac- 
tive spot on the leaf, or migrate upward 
to a more tempting leaf, or in some 
cases may even travel to another plant. 

THE VIOLET AS HOST. 

When cotton dies or becomes untempt- 
ing in the late fall an exodus of red 
spiders from the cotton fields occurs in 
the effort to find more suitable food 
plants. At this time cotton mites may 
be easily found on a number of native 
and cultivated plants, prominent among 
which are cowpeas. tomato. Jamestown 
weed, ironweed, and cultivated violets. 
Most of these plant- die after the frosts, 
but the violet remains somewdiat green 
throughout the winter, and it i-' upon 
dii- plant, probably, that the vast majority of mites overwinter. Out 
of many cases of cotton infestation investigated the vast, majority 
have indicated most clearly that the original source of the pest was 
doubtless this innocent pet of the housewife, the English violet. 
(See fig. •_'.) 

otiiki; in '-is. 

In all. the red spider ha- been found in 1911 upon over 50 species 
of plants, including weed-, ornamental plants, and garden and field 
crop-. Upon most of these the pesl was only occasionally seen, but 
it wa- found commonly throughout the active season upon the I'd 
lowing plant-: Beans, oowpeas, dahlia, ironweed. Jerusalem-oak 
Weil. Jamestown weed, okra, tomato, wild blackberry, and wild 
geranium. 



;•:;.'. '•/•:•:•// ..;': 




o O O o 

o 
o 

°-C3 





Pig, -. — Diagram showing how vio- 
lets growing in dooryard give 
rise to rod Bpider infestation in 
adjoining field. The infestation 
is most severe near the yard. 
This diagram is typical of many 
cases found during 1911. (Orig 
Inal. i 



b THE RED SPIDER ON COTTON. 

HIBERNATION VERSUS WINTERING. 

Some observers have thought that the red spider commonly hiber- 
nates in trash or in the soil in cotton fields, but the past season's 
investigations have produced absolutely no evidence to support this 
idea. During the early spring, before the active season for the red 
spider commenced, trash was several times taken from fields in which 
the infestation had previously been severe and examined with great 
care. A few minute dormant acarids and other forms were thus 
obtained, but no reel spiders could be found in such material. Simi- 
larly, during December, 1911, ample quantities of trash, etc., from 
recently infested fields were carefully examined, but always without 
finding any trace of the red spider. That this pest remains more or 
less active throughout the winter there can be no doubt. Mr. G. A. 
Runner found active adults at Batesburg, S. C, on December 21, 
1909. Mr. H. F. Wilson observed red spiders feeding in early Feb- 
ruary at the same locality. The writer found all stages on violets on 
March 11, and adults as late as December 19, on the same host at 
Batesburg. The finding of the active red spiders during the coldest 
weather is certainly an additional indication that hibernation doe? 
not take place in South Carolina. 

DISPERSION. 

How do red spiders become established upon cotton? They have 
no wings and their legs are very minute. Close observations reveal 
that on the ground they normally travel at the rate of 1 inch per 
15 seconds, which, if maintained, would total 480 feet in 24 hours. 
Red spiders are doubtless occasionally transferred by dogs, chickens, 
other domestic animals, insects, and birds. Strong winds ma}' serve 
occasionally to transfer them from plant to plant. It is the writer's 
firm belief, however, that the chief means of dispersion is the red 
spider's own efforts. When once established in a field they may be 
further distributed by farm hands and by stock while cultivation is 
being carried on. They also spread from plant to plant along the 
interlacing branches, but traps specially prepared with " tangle-foot " 
and placed in the field have proven that individuals commonly crawl 
from plant to plant by way of the stalk and the ground. 

Since the red spider apparently uses no instinct or intelligence in 
finding cotton plants, it follows that the pest must hit upon the cotton 
stalks entirely by chance. The result of this haphazard manner of 
migration must necessarily result often in the penetration of the 
spiders far into the center of fields, thus giving rise to the mistaken 
impression that they had hibernated at these points. 

Furthermore, as the likelihood of the discovery of cotton by the 
spider is doubtless in proportion to the thickness of the '"stand," it 



THE RED SPIDER ON COTTON. / 

should follow that the thick broadcasting of a narrow border strip 
along tlif edge of a field adjoining a source of infestation would serve 
as a trap crop to intercept the majority of migrating spiders. This 
strip should be plowed in as soon as there seems to be danger of a 
general movement to the main held. (For a practical te.st of this 
idea, see under Prevention, p. 10.) 

NATI BE OF I) \M.UiK. 

Cotton seedlings 2 inches bigh were found infested on .May 1. but 
not until dune 1 did the work of the pest become noticeable. The 





I — a, Cross ' normal cotton leaf; h. cross section of cotton leaf Injured by 

the red spider. The puncture Is near lower right-hand corner. Highly magnified, 
oal. i 

presence of the pest on cotton is first revealed by the appearance on 
the upper surface pi the leaf of a blood-red spot. A.s leaves become 
badly infested they redden over -the entire surface, become distorted, 
and drop. The lower leaves are first attacked, but infestation spreads 
upward until often only the bare stalk and one or two terminal 
leave- remain. Such plants almost invariably die. The injury to 
the leaf and the discoloration which follow- the feeding of the mites 
are easily understood by referring to figure '■'>. which represents (a) 
the appearance of healthy cotton leaf-tissues and (&) the condition 
of the tissue after feeding In the pest. A- previously intimated, the 
worsl spots of infestation are usually to be found in close proximity 



8 THE BED SPIDER ON COTTON. 

to yards with borders of violets. Large fields are probably never 
completely damaged, but small fields frequently become wholly 
affected. The crop of one 5-acre field near Leesville, S. C, was 
probably reduced at least 50 per cent by this pest. Local spots with 
from 25 to 100 per cent damage are frequently to be seen. 

NATURAL CONTROLLING AGENCIES. 

Red spider occurrence was most severe throughout July and was 
still at its height on August 1. Within three weeks of the latter 
date, however, the pest had become so greatly diminished that it was 
hardly noticeable and was doing practically no damage. This 
phenomenon indeed happened suddenly, and the agencies which 
worked to produce it are unquestionably of great economic value. 
The toughening of the leaves at that time may have caused many 
mites to desert cotton for other plants, but another factor of much 
more importance was the appearance in abundance of several species 
of insect enemies. 

CLIMATIC INFLUENCES. 

As before mentioned, climatic conditions exert a marked influence 
upon the welfare of the pest. During times of little rainfall and 
high temperature reproduction goes on by leaps and bounds; on 
the other hand, long, heavy rains work havoc to the red spider 
population. In spite of the fact that the red spiders inhabit the 
underside of the leaves, many are washed off by rains and many more 
are destroyed by the upward bombardment of sand particles, which 
may always be seen coating the lower leaves after storms. From 
observations made both early in the season and at the beginning of 
winter it is doubtless true that the young stages are killed by freez- 
ing weather. This naturally prevents any considerable winter in- 
crease, and in addition many adults probably perish. 

INSECT ENEMIES. 

Hot weather, although favoring red-spider development, also en- 
courages the increase of insect enemies, of which several have been 
observed. Were it not for these inconspicuous friends of the farmer 
the depredation to his crops by the red spider would unquestionably 
be far more severe. The following are a few of the more important 
beneficial species observed this season at Batesburg, S. C. 

Triphleps insidivsus Say (fig. 1), a small anthrocorid bug, was 
seen from the beginning of August, and both in the nymphal and 
aduli stages was probably the most effective enemy of the spider. 
Coming upon a red spider like a flash, the adult thrusts its sharp 
proboscis through the pest's back and proceeds quietly to siphon out 



Till- i:ii' S1UD1 R ON COTTON. 




Fig. 4. — Triphlepa Insidiosus, sxu important enemy of tbe 
red spider. Much enlarged. (Original.) 



tin- body contents. The first victim observed was "drained' 1 in 

about five minutes, but each succeeding meal was of shorter dun 

as the appetite became 

satisfied. The actions 

dt' the nymph (fig. 5) 

arc similar, but the in- 
dividuals observed were 

seen only to destroy 

eggs of the spider. In 

this operation the pro- 
boscis was not inserted 

far into the ovum, and 

two minutes sufficed for 

draining an egg. 

A species of Chry- 

sopa or lace-winged fly 

was seen abundantly 

throughout most of the 

summer, the larva of 

which is doubtless very active in reducing the pest. 
Two species of thrips, Eutkrips ftcscus Hind- and E. occidentals 

Pergande, have been determined this season from cotton. They are 

commonly found throughout, 
the season about red spider 
colonies, and may be very in- 
strumental in spider destruc- 
tion. Srolothrips sexmacidata 
Pergande has been recorded as 

• 

an enemy of the red spider by 
Pergande and by Dully. 

Lady-beetle larvae and adults 
of several species were com- 
monly seen on infested Leaves. 
These were usually either 
I .,, , irn lla 9-notata I Ib-i. or 
Hippodamia convt rg> ns Guer., 
Init a small black species, 

§ i/ni nil*) st, thorus i 
1 ..'!•.. n as occasionally observed. 
The larger beetles were prob- 
ably more intent upon cotton aphides, but the last-mentioned sp< 
although late in appearing and not very numerous, seems to be more 
restricted to the cotton mite than arc other spe 




/ \p) I ■ :. ■ ina d • ■ Nymph, 

Greatly enlarged. (Original.) 



10 THE RED SPIDER ON COTTON, 



REMEDIAL MEASURES. 



PREVENTION. 



Control on violets. — First among preventive measures against the 
red spider is that of its control on violets. In most cases, as before 
stated, infested cotton fields upon examination are found to have 
near them infested violet borders. In early June of the past season, 
in one particular instance, violets adjoining fields of past severe 
annual infestation were thoroughly sprayed. It is of great interest 
to record that subsequent infestation in these fields was practically 
negligible. These and similar observations certainly emphasize the 
important part that the violet plays in the seasonal history of the red 
spider. 

( '/( an culture. — Borders of weeds and underbrush about fields 
should be burned or grubbed out. Margining a field close to a spot 
which was heavily infested the previous season there was found to 
occur a thick border of wild geranium, dock, and other weeds which 
at that time contained many red spiders. These weeds were de- 
stroyed by burning over them a heavy application of straw. No 
spiders appeared in the adjoining cotton throughout the season. 

Broadcasted cotton. — An opportunity was accidentally provided of 
testing the value of thickly broadcasting cotton at the boundary of 
a field as a trap crop for red spiders. This cotton, intended as a 
cover crop, intervened between the cotton field proper and a large, 
heavily infested border of violets — a former abundant source of 
migration. The broadcasted cotton became infested and was later 
plowed in. The adjoining field remained free from mites. The suc- 
cess of this experiment would strongly indicate that the cotton trap 
crop is one of the most practical cultural expedients to be used in 
controlling this pest. 

Spacing. — Experiments at Batesburg, S. C. have shown that the 
reel spider commonly travels between plants upon the ground. This 
shows the futility of spacing as a remedial measure. 

Time of planting. — The advantages of early or of late planting 
are not sufficiently clear to justify serious consideration. It would 
seem reasonable, however, to suppose that early planting would en- 
able the plants to attain greater size and vigor by the time of the 
appearance of the spiders and that this would perhaps assist the 
plants in withstanding the weakening effects of the pest. 

Rotation. — In an effort to test the rotational value of other crops, 
cow-peas, corn, beets, and peanuts were planted in or near infested 
areas. In addition, grains, beans, peas, onions, tomatoes, squash, 
watermelon, okra, turnip, lettuce, and other vegetables in infested 
locations have been observed frequently. Excepting the grains and 
peanuts, the red spider has been seen commonly upon all of these. 



THE BED BPIDEB ON COG CON. 11 

On the other hand, should an immune crop be found and employed, 
it is extremely probable that the pes! would reinvade the fields upon 
the return to <-<>tton culture with as irivat ease ami quickness as it 
has done during any previous season, providing the sources of infesta- 
tion were yel at hand. Rotation, then, does not promise to contribute 
toward the solution of the problem. 

Effects of fertilizers. A rather elaborate series of tests with fer- 
tilizers was instituted in an attempt to determine whether the various 
applications assisted cotton to withstand the injurious effects of 
infestation. Since almost no infestation appeared in these test plats 
it was impossible to deduce positive conclusions, l! was very notice- 
able, however, that plant- receiving heavy applications withstood the 
very severe droughl conditions which prevailed in South Carolina in 
11)11 conspicuously better than did plant- which were not so treated. 
It seems reasonable to suppose, therefore, that plant- which, have 
U'en fortified bj a libera] quantity ol' fertilizer will be assisted, upon 
occurrence of severe infestation, in resisting it- effects. 

l;l PRESSION. 

We have just discussed cultural measures which may help to pre- 
vent infestation. We will now consider what may he done to combat 
the pest when it has already gained entrance to a field. 

Pulling infested plants. — The experiment was made in one Held of 
pulling up and destroying the first few plant- which -bowed infesta 
tion. In thi> particular case the operation was repeated three times. 
Care was taken to find every plant showing the characteristic red 
spots, and these were carried from the field and burned. The result 
was most satisfactory, and the pest was completely eradicated. 

[f infestation has spread until a considerable patch has become 
involved it might be advisable, in the case of a large Held, to plow 
up the a fleet ed portion in order to save the balance of the field. Such 
a drastic measure, however, should only be resorted to in extreme 
cases, and the planter concerned must he the judge of its desirability. 

Insecticides.— In all. l'<'> spray combinations were thoroughly tested 
under conditions entirely natural. The field used for this purpose 
was ahoitt 1 acre in extent, and infestation had become both verj gen- 
eral and very severe. A strip through the middle of the field, crossing 
each sprayed plat, was left unsprayed to serve a- a cheek. Since no 
substance was discovered which could safely he used i" destroy all 
eggs in one application, it was found necessary to spray twice with 
an interval of -ix or -even days, so a- to destroy the hatching larvae. 
The killing ability of all these sprays was computed, and the per- 
centages range from 100 to 0. Each of the following six combina- 
tions (see Table II) wa- found to be very satisfactory. These are 
presented to indicate the manner of preparation, together with the 



12 



THE RED SPIDER ON COTTON. 



cost of 100 gallons of each. If one of these were to be used in 
preference to all others it should undoubtedly be potassium sulphid. 
This insecticide commends itself from every standpoint — cheapness, 
simplicity of preparation, continued readiness for use, ability to kill 
quickly, and safety of foliage. Altogether it seems to be an ideal 
red-spider spray. It was found that 100 gallons, when applied as a 
misty spray, about sufficed to treat an acre of average-sized cotton. 

Table II. — Some satisfactory sprays for the red spider. 



Spray 
No. 



I 
II 

III 
IV 

V 

VI 



Formula and items. 



Potassium sulphid, 3 pounds, at 25 cents 

Water, 100 gallons. 

Flowers of sulphur, 15 pounds, at 4 cents] | $0. f>0 

Fresh lime, 20 pounds, at 4 cents /boiled< 80 

Water, 100 gallons ) ( 

Miscible oil, 5 gallons, at $1 

Water to make 100 gallons (1 to 20). 

Potassium permanganate, 16| pounds, at 50 cents 

Water to make 100 gallons (2 per cent solution). 

Miscible oil, 2\ gallons, at $1 $2. 50 

Black-leaf tobacco extract, 40%, £ gallon, at $1.25 per pound 2. 00 



Flowers of sulphur, 28 pounds, at 4 cents $1. 12 

Soft soap, 14 ounces, at 40 cents per pound 35 

Water to make 100 gallons. 



Total 
cost. 



$0.75 

1.40 
5.00 

8.25 
4.50 



Per cent 
killed. 



100 
100 

100 



99 



SI .M.MARY. 

The female red spider, appearing to the naked eye like a dot of 
reddish ink from the point of a fine pen, lays about 50 or 60 round, 
colorless eggs, which hatch in summertime in about four days. 

The colorless, newborn spider has six legs, feeds at once, and molts 
in two days to the primary nymph. 

This first nymphal stage (and all later stages) possesses eight 
legs, and has become larger in size and darker in color. In two more 
days (in summer) it, in turn, molts to the secondary nymph. 

The second nymphal stage lasts two days, at the end of which 
time, after molting, the fully formed adult emerges. Mating occurs 
at once and egg laying commences immediately afterwards. 

Thus, one generation requires in summer weather in South Caro- 
lina about 10 or 11 days. There are probably about 15 generations 
in an average year in that locality. 

The red-spider colonies live on the underside of the cotton leaves, 
and their constant feeding causes blood-red spots to appear on the 
tops of the leaves. The effect upon the cotton plant is that the 
leaves drop, one by one, until usually the plant dies. 

The pest increases and spreads most rapidly in hot, dry weather 
until (toward the end of July) several acres of a field may become 
badly damaged. 



THE RED SPIDEB OK COI CON. l;i 

Several insects have been discovered which destroy many mites, 
and are thus of great benefil to the planter. 

At the end of the cotton-growing season most of tin- red spiders 
migrate afoot in search of greener plants, the majority of those 
which survive settling ultimately upon the cultivated violet. 

RECOMMENDAl [ONS. 

(1) Clean culture. — Burn or grub out all weeds and underbrush 
about cotton Gelds and practice fall plowing so far as possible. 

[..') Control on violets. -Spray or destroy suspected riolet plants 
in order to remove the sources of red spider infestation. 

(3) Broadcasted trap borders. — Thickly so'w cotton along mar- 
gins of fields at point- where infestation has appeared on former 
occasions, ami plow these in about June 1. so a- to intercept and 
destroy the invading mites. 

I/) Pulling "first infested stalks. — Maintain a careful watch of 
fields so that the first attacked plants may l>e detected, removed, and 
burned, thus preventing further spread. 

(5) Spraying. — Apply one of the insecticide-- recommended above 
to the infested portion of a field before occurrence becomes too gen- 
eral to prohibit its use. Two application- should be made; the first 
to destroy the living mites, and the second, a week later, to kill the 
recently hatched individual-- which were eggs at the time of the first 
spraying. 

finally, the opinion will be ventured that the red spider is not a 
difficult pesi to combat. Unlike many other pests, it has no wings 
and spread- mainly by means of it- tiny legs. Migration does not 
extend far from its winter quarters. This make- every man*- prob- 
lem virtually his own. In other words, if hi- infestation ha- always 
come from a certain spot upon his premises, proper attention to this 
spot will yield him results in spite of the negligence of his neighbors. 

Approved : 
James Wilson, 

>. ( /, tary ,>i . [grit ultu 

Washington, D. ('.. February I',. 1012. 



UNIVERSITY OF FLORIDA 



II II 



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